Organic light-emitting device

ABSTRACT

An organic light-emitting device includes a substrate, on which a transparent electrode and a further electrode are applied. An organic light-emitting layer is arranged between the electrodes. At least one optical scattering layer is arranged on a side of the transparent electrode facing away from the organic light-emitting layer.

This patent application is a national phase filing under section 371 ofPCT/EP2012/072230, filed Nov. 9, 2012, which claims the priority ofGerman patent application 10 2011 086 168.8, filed Nov. 11, 2011, eachof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

An organic light-emitting device is provided.

BACKGROUND

In the case of conventional organic light-emitting diodes (OLEDs), onlysome of the generated light is directly coupled out. The rest of thelight generated in the active region is distributed to various losschannels, for instance in light which is guided in the substrate, in atransparent electrode and in organic layers by means of wave guideeffects, and in surface plasmons which can be generated in a metallicelectrode. The wave guide effects occur in particular by reason of thedifferences in the refractive index at the boundary surfaces between theindividual layers and regions of an OLED. In particular, the light whichis guided in the loss channels cannot be coupled out from an OLEDwithout additional technical measures.

In order to increase the coupling-out of light and thus the radiatedlight power, measures are known in order to couple out the light, whichis guided in a substrate, into radiated light. For this purpose, filmshaving scatter particles or films having surface structures, such asmicrolenses, are used, e.g., on the substrate outer side. It is alsoknown to provide direct structuring of the substrate outer side or tointroduce scatter particles into the substrate. Some of theseapproaches, e.g., the use of scattering films, are already usedcommercially and can be scaled up in particular in the case of OLEDs,which are designed as illumination modules, in relation to the radiatingsurface. However, these approaches for coupling out light have thesignificant disadvantages that the coupling-out efficiency is limited toabout 60% to 70% of the light guided in the substrate and that theappearance of the OLED is significantly influenced, as a milky,diffusely reflecting surface is produced by the applied layers or films.

Approaches are also known for coupling out the light which is guided inorganic layers or in a transparent electrode. However, these approacheshave hitherto not become established in a commercial sense in OLEDproducts. For example, the document Y. Sun, S. R. Forrest, NaturePhotonics 2,483 (2008) proposes the formation of so-called “low-indexgrids”, wherein structured regions having a material with a lowrefractive index are applied onto a transparent electrode. Furthermore,it is also known to apply highly refractive scattering regions under atransparent electrode in a polymeric matrix, as described, e.g., in U.S.patent application 2007/0257608. In this case, the polymeric matrixgenerally has a refractive index in the region of 1.5 and is appliedusing wet chemistry. Furthermore, so-called Bragg grids or photoniccrystals having periodic scattering structures with structure sizes inthe wavelength range of the light are also known, as described, e.g., inthe documents Ziebarth et al., Adv. Funct. Mat. 14, 451 (2004) and Do etal., Adv. Mat. 15, 1214 (2003).

OLEDs having a large luminous surface often encounter the problem oflight density inhomogeneity as the distance from electrical contactsincreases. This problem can be improved by using current-conductingstructures, so-called “bus bars” within the active luminous surface.However, structures such as these are visible in the light-emittingpattern of an OLED and for this reason are undesirable.

SUMMARY OF THE INVENTION

At least one example of specific embodiments is to provide an organiclight-emitting device.

In accordance with at least one embodiment, an organic light-emittingdevice has on a substrate a transparent electrode and a furtherelectrode, between which an organic functional layer stack is arranged.The organic functional layer stack has an organic light-emitting,electroluminescent layer. The organic light-emitting device can beformed in particular as an organic light-emitting diode (OLED).

The organic functional layer stack can have layers comprising organicpolymers, organic oligomers, organic monomers, organic, small,non-polymeric molecules (“small molecules”) or combinations thereof. Inparticular, it can be advantageous if the organic functional layer stackhas a functional layer which is designed as a hole transport layer, inorder to permit effective hole injection into the light-emitting layer.For example, tertiary amines, carbazole derivatives, conductivepolyaniline or polyethylene dioxythiophene can prove to be advantageousas materials for a hole transport layer. Materials which have radiationemission by reason of fluorescence or phosphorescence, e.g.,polyfluorene, polythiophene or polyphenylene or derivatives, compounds,mixtures or copolymers thereof, are suitable as materials for thelight-emitting layer. Furthermore, the organic functional layer stackcan have a functional layer which is formed as an electron transportlayer. Furthermore, the layer stack can also have electron and/or holeblocking layers. The organic functional layer stack can also have aplurality of organic light-emitting layers which are arranged betweenthe electrodes.

With regard to the basic structure of an organic light-emitting device,e.g., with regard to the structure, the layer composition and thematerials of the organic functional layer stack, reference is made toInternational patent publication WO 2010/066245 A1 which is herebyexpressly incorporated by reference in particular in relation to thestructure of an organic light-emitting device.

The electrodes can each be formed over a large area. This permitslarge-area radiation of the electromagnetic radiation generated in theorganic light-emitting layer. The term “large-area” can mean that theorganic light-emitting device has an area of greater than or equal toseveral square millimeters, preferably greater than or equal to onesquare centimeter and particularly preferably greater than or equal toone square decimeter.

Furthermore, an encapsulation arrangement can also be arranged above theelectrodes and the organic functional layer stack. The encapsulationarrangement can be designed preferably in the form of a thin-layerencapsulation.

In the present case, an encapsulation arrangement formed as a thin-layerencapsulation is understood to be an apparatus which is suitable forforming a barrier against atmospheric substances, in particular againstmoisture and oxygen and/or against further damaging substances such ascorrosive gases, e.g., hydrogen sulphide. In other words, the thin-layerencapsulation is formed in such a manner that at the most only verysmall quantities of atmospheric substances can penetrate it. In the caseof the thin-layer encapsulation, this barrier effect is producedsubstantially by barrier layers and/or passivation layers which aredesigned as thin layers and form part of the encapsulation arrangement.The layers of the encapsulation arrangement generally have a thicknessof less than or equal to a few 100 nm.

In particular, the thin-layer encapsulation can comprise or consist ofthin layers which are responsible for the barrier effect of theencapsulation arrangement. The thin layers can be applied, e.g., by anatomic layer deposition (ALD) process. Suitable materials for the layersof the encapsulation arrangement are, e.g., aluminum oxide, zinc oxide,zirconium oxide, titanium oxide, hafnium oxide, lanthanum oxide andtantalum oxide. Preferably, the encapsulation arrangement has a layersequence having a plurality of thin layers which each have a thicknessbetween one atom layer and 10 nm inclusive.

Alternatively or in addition to thin layers produced by ALD, theencapsulation arrangement can have at least one or a plurality offurther layers, i.e., in particular barrier layers and/or passivationlayers which are deposited by thermal vapor deposition or by aplasma-assisted process, such as sputtering or plasma-enhanced chemicalvapor deposition (PECVD). Suitable materials for this can be theaforementioned materials, and silicon nitride, silicon oxide, siliconoxynitride, indium tin oxide, indium zinc oxide, aluminum-doped zincoxide, aluminum oxide and mixtures and alloys of said materials. The oneor plurality of further layers can have, e.g., in each case a thicknessbetween 1 nm and 5 μm and preferably between 1 nm and 400 nm inclusive.

In accordance with a further embodiment, the substrate comprises one ora plurality of materials in the form of a layer, a plate, a film or alaminate which are selected from glass, quartz, synthetic material,metal and silicon wafer. In a particularly preferred manner, thesubstrate comprises, or is made from, glass, e.g., in the form of aglass layer, glass film or glass plate.

In accordance with a further embodiment, the substrate is formed in atransparent manner and the transparent electrode is arranged between thesubstrate and the organic light-emitting layer, so that light generatedin the light-emitting layer can be radiated through the transparentelectrode and the substrate. This type of organic light-emitting devicecan also be defined as a so-called “bottom emitter”.

In accordance with a further embodiment, a cover layer is arranged, asseen from the substrate, on the organic functional layer stack and theelectrodes, so that the electrodes and the organic functional layerstack are arranged with the organic light-emitting layer between thesubstrate and the cover layer. The cover layer can also be defined as a“superstrate” in terms of its arrangement in comparison with thesubstrate.

In accordance with a further embodiment, the cover layer is formed in atransparent manner and the transparent electrode is arranged between theorganic light-emitting layer and the cover layer, so that lightgenerated in the light-emitting layer can be radiated through thetransparent electrode and the cover layer. This type of organiclight-emitting device can also be defined as a so-called “top emitter”.The further electrode which is arranged on the side of the organicfunctional layer stack facing towards the substrate is designed in areflective manner for an organic light-emitting device formed as a “topemitter”.

The cover layer can comprise, e.g., one or a plurality of the materialspreviously described in connection with the substrate. In a particularlypreferred manner, the cover layer comprises a glass layer, glass film orglass plate.

The cover layer can have encapsulating properties and can be part of anencapsulation arrangement or can be formed as an encapsulationarrangement. Furthermore, it is also possible for the cover layer to beapplied only as mechanical protection, e.g., as scratch-protection. Theorganic light-emitting device can comprise, in addition to the coverplate, an above-described encapsulation arrangement, in particular athin-layer encapsulation, above which, as seen from the substrate, thecover layer is arranged.

In accordance with a further embodiment, at least one optical scatteringlayer is arranged on a side of the transparent electrode facing awayfrom the organic light-emitting layer.

In accordance with a further embodiment, the at least one opticalscattering layer is arranged between the transparent electrode and thesubstrate which is formed in a transparent manner.

In accordance with a further embodiment, the at least one opticalscattering layer is arranged on a side of the substrate which faces awayfrom the transparent electrode and is formed in a transparent manner.

In accordance with a further embodiment, the at least one opticalscattering layer is arranged between the transparent electrode and thecover layer which is formed in a transparent manner.

In accordance with a further embodiment, the at least one opticalscattering layer is arranged on a side of the cover layer which facesaway from the transparent electrode and is formed in a transparentmanner.

It is also possible for the organic light-emitting device to have aplurality of optical scattering layers in accordance with combinationsof the aforementioned embodiments.

In comparison with a material which is defined as a normally refractivematerial and has a refractive index of 1.5, the scattering layer canhave a material which is defined in this case as a more highlyrefractive material and has a refractive index in a region of greaterthan or equal to about 1.6 and less than or equal to about 1.7 to 1.8,or can have a material which is defined in this case as a highlyrefractive material and has a refractive index of greater than 1.8. Therefractive indices described here and hereinafter apply for a wavelengthof, e.g., 600 nm. For other wavelengths, a stated refractive index valuecan also change by reason of material dispersion.

Furthermore, the scattering layer can comprise, or can be formed from, amatrix material and scatter particles, wherein the scatter particlespreferably have a refractive index which is different from the matrixmaterial. In the case of a scattering layer having a matrix material andscatter particles, the refractive indices of the scattering layer asdescribed above and hereinafter relate to the matrix material.

By means of the at least one optical scattering layer which, as seenfrom the organic light-emitting layer, is arranged on the opposite sideof the transparent electrode, the coupling-out of light from the organiclight-emitting device can be effected by a reduction in that proportionof light which is guided in the layers of the device by wave guideeffects. Furthermore, it can also be possible to achieve an improvementin the luminous density homogeneity and a reduction in the luminousdensity inhomogeneity. It can thereby also be possible, in particular inthe case of a scattering layer arranged on the side of the substrate orthe cover layer facing away from the transparent electrode, tocompensate for process fluctuations in relation to luminous densityinhomogeneity and/or the emission color by means of targeted adaptationof the scattering layer.

The scattering effect of the at least one scattering layer can beinfluenced, e.g., by varying the concentration of the scatter particlesin the matrix material. Furthermore, the scattering effect can also beinfluenced by varying the number of scatter particles on the activesurface of the organic light-emitting device. In particular, thescattering layer can have, e.g., a varying thickness and/or a varyingconcentration of the scatter particles in the matrix material, so thatthe scattering effect can be influenced in the entire film and alsoinside the film by means of which the at least one optical scatteringlayer is formed. By changing the scattering effect in a targeted mannerwithin the optical scattering layer, e.g., a continuous progression ofthe scattering effect can be achieved. The light is thereby coupled outmore effectively at certain, intended locations, whereby, e.g., luminousdensity inhomogeneities can be compensated for in a targeted manner.Furthermore, it is also possible to provide only individual regions witha scattering effect or to provide individual regions with a strongerscattering effect than other regions, whereby effects such as thedisplay of writing or symbols such as pictograms becomes possible bymeans of intentionally increased inhomogeneities or other structuredluminous impressions within the luminous image, i.e., on the activesurface. More light is thereby radiated from the regions in which thescattering effect is higher than from regions in which the scatteringeffect is lower or which have no scattering effect.

Therefore, by means of a scattering layer which has a varyingarrangement of scatter particles, depending upon the arrangement of thescatter particles it is possible to achieve either a homogenization ofthe luminous image or even a target inhomogeneity of the luminous image.For example, one of the electrodes or both electrodes can each beelectrically contacted by a contact element which is arranged preferablyat the edge of the active surface. By reason of the material and/or thethickness of the respective electrode, a voltage drop can be presentalong the electrode as the distance from the contact element increases,whereby the number of charge carriers which are injected into theorganic functional layer stack can decrease as the distance to thecontact element increases. In order to compensate for the correspondingdecrease in the luminous density as the distance from the contactelement increases, the scatter particles in the at least one opticalscattering layer can have a concentration which increases as thedistance from the contact element increases.

The at least one optical scattering layer can be applied, e.g., asself-supporting film, in particular on the side of the substrate orcover layer facing away from the transparent electrode. Aself-supporting layer is defined here and hereinafter as a layer whichis produced separately prior to the arrangement on the substrate orcover layer. Furthermore, it is also possible to lay the at least onescattering layer as described above “inwardly” and to arrange it at thatlocation, i.e., for a top emitter, e.g., between a thin-filmencapsulation and the cover layer which can be formed by a cover glass,for bottom emitters, between the substrate and the transparentelectrode. Depending upon the material of the scattering layer, it maybe necessary in particular in the case of such internal scatteringlayers to arrange, between the scattering layer and the transparentelectrode, a further barrier in addition to the encapsulationarrangement which is formed, e.g., by a further thin-film encapsulationdescribed above. In particular, in the case of materials for the opticalscattering layer which are applied from the liquid phase, it can beparticularly advantageous to arrange such a barrier or encapsulationlayer between the scattering layer and the transparent electrode.

In the case of layers which are processed in a non-liquid manner asdescribed further below, e.g., consisting of inorganic materials, it canalso be possible that no such additional barrier is required, e.g., inthe case of a scattering layer which has a highly refractive materialconsisting of glass, an oxide or a nitride which themselves normallyhave a barrier effect.

An external scattering layer defines here and hereinafter an opticalscattering layer which is arranged on the side of the substrate or coverlayer facing away from the transparent electrode, whereas an opticalscattering layer defined as an internal scattering layer is arrangedbetween the transparent electrode and the substrate or between thetransparent electrode and the cover layer.

Depending on whether the scattering layer is arranged on the inside oroutside, various materials from different refractive index ranges haveproven to be particularly advantageous. If the scattering layer isapplied externally on the substrate or cover layer, the scattering layercan preferably have a refractive index in the region of about 1.5, i.e.,a normally refractive material. In particular, in this case thefollowing polymers have proven to be advantageous as the matrixmaterial: polycarbonate, polyethylene naphthalate, polyethyleneterephthalate, polyurethane and an acrylate such as polymethylmethacrylate. The scatter particles preferably comprise a material whichhas a refractive index different from the matrix material, e.g., thescatter particles can comprise aluminum oxide, titanium oxide, zirconiumoxide, silicon oxide and/or pores. Pores are defined here andhereinafter as cavities which, e.g., can be filled with gas, i.e.,filled with air.

In the case of an internal scattering layer, the matrix material usedcan be same as for an external scattering layer. Furthermore, aninternal scattering layer can also comprise the aforementioned scatterparticle materials or scatter particle embodiments.

In particular, an internal scattering layer can have a refractive indexwhich is at least equal to and preferably greater than a layerthickness-weighted average refractive index of the layers of the organicfunctional layer stack. In the case of internal scattering layer, theuse of more highly refractive or highly refractive materials can beparticularly advantageous, as the coupling-out of light can be increasedstill further as a result. For example, the scattering layer cancomprise a matrix material in the form of a highly refractive layerwhich is applied from the liquid phase and which comprises a polymerhaving metal oxides distributed therein, such as are available, e.g.,from the company BrewerScience under the designation OptiNDEX-series.Furthermore, in addition to or as an alternative to the aforementionednormally refractive polymers, the scattering layer can also comprise,e.g., an epoxide as the matrix material.

Furthermore, in order to increase the refractive index of the matrixmaterial, an additive can be contained therein which consists of a morehighly refractive material, e.g., a metal oxide such as titaniumdioxide. The additive is present preferably in the form of nanoparticleswhich have a size of less than 50 nm. Nanoparticles of such a size whichis in a range considerably lower than the wavelength of the lightgenerated in the organic light-emitting layer do not act as individualscatter particles in particular for visible light.

Furthermore, it is also possible that the scattering layer comprises asol-gel material having a refractive index of greater than 1.8 and/or aninorganic material having a refractive index of greater than 1.8. Suchan inorganic material can be formed, e.g., by a highly refractive glassor by a highly refractive oxide or nitride, e.g., titanium dioxide,silicon nitride, tantalum oxide or zirconium oxide.

In accordance with a further embodiment, the scatter particles have asize of greater than or equal to 200 nm and less than or equal to 5000nm. Such scatter particles can achieve a scattering effect by beingintroduced into the matrix material having a refractive index differentfrom the scatter particles. The scatter particles can thereby have ahigher or lower refractive index than the matrix material. Highlyrefractive scatter particles can comprise, e.g., titanium dioxide orzirconium dioxide, whereas low-refractive scatter particles cancomprises, e.g., silicon dioxide or can be formed by pores. It isparticularly advantageous if the refractive indices of the matrixmaterial and of the scatter particles as well as the concentration ofthe scatter particles are selected such that the scattering effect(“haze”) of the entire scattering layer is not less than 20%.

In accordance with a further embodiment, the scattering layer can beapplied, e.g., by porous printing, screen printing, spin-coating orspray-coating. It is thereby also possible to produce, e.g., a gradientin the scattering effect by a varying number or concentration of thescatter particles. A linear gradient can be achieved, e.g., by varyingthe thickness of the scattering layer by lowering the doctor blade in aprinting process. A radial concentration gradient of the scatterparticles can be achieved, e.g., by spin-coating and by means of theeffective centrifugal forces. Any gradient can, e.g., also be producedby printing processes. For example, points of the wet scattering layercan be printed on with a different density for each surface, which flowinto one another through a temperature film and produce a continuousscattering film or a continuous scattering layer having a differentlayer thickness. Furthermore, it is also possible to achieve anyconcentration gradient of the scatter particles, in that, e.g., thematrix material is applied in a uniform film and a laterally varyingdensity of scatter particles is applied thereon. The scatter particlescan thereby be applied, e.g., by printing, for instance inkjet printing,or spraying. After being applied, the scatter particles sink into thematrix material and produce laterally different scattering effects byreason of their laterally varying density.

In accordance with a further embodiment, the scattering layer comprisesat least one additive which is UV-absorbent. As a result, the organiclayers of the organically functional layer stack can be protectedagainst UV radiation. For this purpose, the additive can comprise, e.g.,titanium dioxide or an organic material which absorbs UV radiation,e.g., one or a plurality of the following materials:2-hydroxybenzophenone, 2-hydroxyphenyl benzotriazole, salicylic acidester, cinnamic acid ester derivative, resorcinol monobenzoate, oxalicacid anilide, p-hydroxybenzoic acid ester.

In accordance with a further embodiment, the scattering layer comprisesat least one additive which has a high thermal conductivity, inparticular a thermal conductivity which is greater than the thermalconductivity of the matrix material. For this purpose, the additive cancomprise e.g. particles having one or a plurality of the followingmaterials: aluminum nitride, silicon carbide and magnesium oxide. Thesematerials can have a thermal conductivity of up to 590 W/mK.

In accordance with a further embodiment, the transparent electrodecomprises or consists of a transparent conductive oxide. Transparentconductive oxides (TCO) are transparent, conductive materials, generallymetal oxides such as, e.g., zinc oxide, tin oxide, cadmium oxide,titanium oxide, indium oxide or indium tin oxide (ITO). In addition tobinary metal oxygen compounds, such as, e.g., ZnO, SnO₂ or In₂O₃,ternary metal oxygen compounds, such as, e.g., Zn₂SnO₄, CdSnO₃, ZnSnO₃,MgIn₂O₄, GaInO₃, Zn₂In₂O₅ or In₄Sn₃O₁₂ or mixtures of differenttransparent conductive oxides also belong to the group of TCOs.Furthermore, the TCOs do not necessarily correspond to a stoichiometriccomposition and can also be p-doped or n-doped.

In accordance with a further embodiment, the transparent electrodecomprises or is made from ITO, ZnO and/or SnO₂. In particular, thetransparent electrode can have a thickness of greater than or equal to50 nm and less than or equal to 200 nm.

Furthermore, it is possible for the transparent electrode to comprise atransparent metal oxide, applied from a solution.

Furthermore, the transparent electrode can comprise a metal layer or ametal film having a metal or an alloy, e.g., having one or a pluralityof the following materials: Ag, Pt, Au, Mg, Ag:Mg.

In accordance with a further embodiment, the transparent electrode isformed as a so-called percolation electrode and in particular as aso-called percolation anode. A percolation electrode can preferablycomprise or be made from the following materials: metallic nano wires,e.g., having or consisting of Ag, Ir, Au, Cu, Cr, Pd, Pt or acombination thereof; semiconducting nano wires, e.g. having orconsisting of InAs and/or Si which furthermore can also be doped;graphene or graphene particles; carbon nanotubes.

In accordance with a further embodiment, the transparent electrodecomprises one or a plurality of the aforementioned materials incombination with a conductive polymer, e.g.,poly-3,4-ethylenedioxythiophene (PEDOT) and/or polyaniline (PANI) and/orwith a transition metal oxide and/or in the case of a metallictransparent electrode or a percolation electrode having a transparentconductive oxide applied from the liquid phase.

In a preferred embodiment, the transparent electrode is formed as ananode and comprises one or a plurality of the aforementioned materials.The further electrode is then formed as a cathode.

In accordance with a further embodiment, the further electrode is formedin a reflective manner and comprises, e.g., a metal which can beselected from aluminum, barium, indium, silver, gold, magnesium, calciumand lithium as well as compounds, combinations and alloys thereof. Inparticular, the reflective further electrode can comprise Ag, Al oralloys therewith, e.g., Ag:Mg, Ag:Ca and Mg:Al. The reflective electrodecan be formed in particular as a cathode. Alternatively or in addition,the reflective electrode can also comprise one of the aforementioned TCOmaterials.

In accordance with a further embodiment, the further electrode is alsotransparent. The transparent further electrode can comprise features andmaterials, as described in connection with the transparent electrode. Inparticular, the organic light-emitting device can be formed with twotransparent electrodes as a translucent OLED which can radiate light onboth sides. At least two scattering layers can also be arranged ondifferent sides of the organic light-emitting layer. In particular,embodiments previously described in the case of an OLED which emits onboth sides can be combined in relation to the at least one scatteringlayer on the substrate side and on the side of the cover layer.

In the case of the organic light-emitting device described in this case,the at least one optical scattering layer in accordance with thepreviously described embodiments renders it possible to achieve anincrease in efficiency and a luminous density homogenization incomparison with OLEDs without such an additional scattering layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, advantageous embodiments and developments will beapparent from the exemplified embodiments described hereinafter inconjunction with the figures, in which:

FIGS. 1A to 1D show schematic views of organic light-emitting devices inaccordance with several exemplified embodiments;

FIG. 2 shows a schematic view of an organic light-emitting device inaccordance with a further exemplified embodiment;

FIGS. 3A and 3B show schematic views of varying scatter particleconcentrations of the scattering layer;

FIGS. 4A and 4B show schematic views of a method for producing ascattering effect gradient; and

FIGS. 5A to 5C show schematic views of a further method for producingscattering effect gradients in accordance with a further exemplifiedembodiment.

In the exemplified embodiments and figures, like elements, or elementsacting in a similar or identical manner, can be provided with the samereference numerals in each case. The illustrated elements and the sizeratios of the elements with respect to each other are not to be regardedas being to scale. Rather, individual elements, such as, e.g., layers,components, devices and regions, may be illustrated excessively large toprovide a clearer illustration and/or for ease of understanding.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1A to 1D show various exemplified embodiments for organiclight-emitting devices 100, 101, 102, 103.

In the case of all of these exemplified embodiments, the organiclight-emitting devices 100, 101, 102, 103 comprise a substrate 1, onwhich an organic functional layer stack 4 having an organiclight-emitting layer 5 is arranged between a transparent electrode 2 anda further electrode 3. Arranged thereabove is an encapsulationarrangement 6 for protecting the organic layers. The encapsulationarrangement 6 is designed in a particularly preferable manner as athin-layer encapsulation as described in the general part.

In the exemplified embodiments of FIGS. 1A and 1B, the substrate 1 istransparent in each case, e.g., in the form of a glass plate or glasslayer. Applied to this glass plate or glass layer is the transparentelectrode 2 which comprises, e.g., a transparent conductive oxide, atransparent metal oxide or another material—stated above in the generalpart—for the transparent electrode or combinations thereof. Inparticular, the transparent electrode 2 is formed as an anode in theillustrated exemplified embodiments. The organic light-emitting devices100, 101 are thus designed as bottom emitters and in operation radiatelight through the transparent electrode 2 and the transparent substrate1.

In the illustrated exemplified embodiments, the further electrode 3 isformed in a reflective manner and comprises in particular a metalmentioned above in the general part. The organic functional layer stack4 having the organic light-emitting layer comprises, e.g., a holeinjection layer, a hole transport layer, an electron blocking layer, ahole blocking layer, an electron transport layer and/or an electroninjection layer which are suitable for conducting holes or electrons tothe organic light-emitting layer 5 or for blocking the respectivetransport. Suitable layer structures for the organic functional layerstack 4 are known to the person skilled in the art and are therefore notdescribed further here.

In the exemplified embodiment in accordance with FIG. 1A, the organiclight-emitting device 100 comprises an optical scattering layer 7 on theside of the substrate 1 facing away from the transparent electrode 2.The external scattering layer 7 comprises a normally refractive materialhaving a refractive index in the region of about 1.5, e.g., a polymermaterial such as polymethyl methacrylate, polycarbonate, polyethylenenaphthalate, polyethylene terephthalate, polyurethane or a combinationthereof which forms a matrix material of the scattering layer 7. Bymeans of such a material, the coupling-out of light guided in thesubstrate 1 by wave guide effects can be achieved by reducing the totalreflection at the boundary surface between the substrate 1 and thescattering layer 7. Furthermore, the scattering layer 7 comprisesscatter particles in the matrix material which have a refractive indexdifferent from the matrix material, as described further below.

The organic light-emitting device 101 in accordance with the exemplifiedembodiment in FIG. 1B comprises, in comparison with the exemplifiedembodiment of FIG. 1A, a so-called internal scattering layer 7, i.e., ascattering layer 7 which is arranged between the substrate 1 and thetransparent electrode 2. The scattering layer 7 can comprise the samematerials as the scattering layer 7 in accordance with the exemplifiedembodiment of FIG. 1A. However, in a particularly preferred manner thescattering layer 7 in the exemplified embodiment in accordance with FIG.1B comprises a more highly refractive or highly refractive matrixmaterial, as described above in the general part. For example, thescattering layer 7 can also comprise an epoxide in addition or as analternative to the aforementioned polymers. Alternatively or inaddition, the scattering layer 7 can comprise as the matrix material ahighly refractive polymer which is available, e.g., from the companyBrewerScience under the designation OptiNDEX.

Furthermore, the matrix material can comprise an additive for adaptingand in particular for increasing the refractive index, such as, e.g.,titanium oxide nanoparticles having a size of less than 50 nm.Furthermore, the scattering layer 7 in FIG. 1B can comprise a sol-gelmatrix material having a refractive index of greater than 1.8. It isalso possible for the scattering layer 7 to comprise an inorganic matrixmaterial, e.g., a highly refractive glass or oxide or nitride, such astitanium oxide, silicon nitride, tantalum oxide or zirconium oxide.

For materials for the scattering layer 7 which are applied from theliquid phase, an additional encapsulation layer, e.g., in the form of athin-layer encapsulation 8, can be arranged, as shown in FIG. 1B,between the scattering layer 7 and the transparent electrode 2, in orderto protect the organic layers of the organic functional layer stack 4against the ingress of damaging substances through the scattering layer7.

The organic light-emitting devices 102 and 103 in accordance with theexemplified embodiments of FIGS. 1C and 1D are formed as so-called topemitters, in which the scattering layer 7 is arranged on the side of theorganic light-emitting layer 5 facing away from the substrate 1.

In FIG. 1C, the scattering layer 7 is arranged as an external layer on acover layer 9 which, as seen from the substrate 1, is arranged above theorganic functional layer stack 4. The cover layer 9 is formed in atransparent manner, e.g., in the form of a glass layer or a glass platewhich can be formed as an encapsulation or even as scratch-protection.Furthermore, the transparent electrode 2 is arranged between thelight-emitting layer 5 and the cover layer 9, so that the lightgenerated in the organic light-emitting layer 5 can be radiated throughthe transparent electrode 2, the encapsulation arrangement 6, the coverlayer 9 and the external scattering layer 7 arranged thereabove.

The organic light-emitting device 103 in accordance with the exemplifiedembodiment of FIG. 1D comprises, in comparison with the exemplifiedembodiment of FIG. 1C, an internal scattering layer 7 between the coverlayer 9 and the transparent electrode 2 and in particular between thecover layer 9 and the encapsulation arrangement 6.

The scattering layer 7 in the exemplified embodiments in accordance withFIGS. 1C and 1D can comprise materials, as described for the scatteringlayers 7 of FIGS. 1A and 1B.

The scattering effect of the scattering layer 7 in the illustratedexemplified embodiments will be achieved by introducing the scatterparticles into the matrix material of the scattering layer 7. Thescatter particles have a size of greater than or equal to 200 nm andless than or equal to 5000 nm and a refractive index which is differentin comparison with the matrix material. For example, the scatterparticles can have a higher refractive index than the matrix material.In particular, scatter particles which consist, e.g., of titanium oxideor zirconium oxide are suitable for this purpose. It is also possiblefor the scatter particles to have a lower refractive index than thematrix material. The scatter particles can consist, e.g., of silicondioxide or can be formed as pores, e.g., as pores which are filled withair.

Furthermore, the scattering layers 7 of the illustrated exemplifiedembodiments can have additives present therein such as, e.g.,UV-absorbent materials and/or materials having a thermal conductivitywhich is greater than the thermal conductivity of the matrix material.The additives can comprise in particular materials, as described abovein the general part.

In addition to the illustrated exemplified embodiments of FIGS. 1A to1D, an organic light-emitting device can also comprise at least two ormore scattering layers which are arranged at the positions shown inFIGS. 1A to 1D.

FIG. 2 shows such an organic light-emitting device 104 which has morethan one scattering layer and, purely by way of example, has fourscattering layer 71, 72, 73, 74 which are arranged on the substrate sideand on the side of the cover layer 9. The organic light-emitting device104 thus corresponds to a combination of the exemplified embodiments ofFIGS. 1A to 1D. In particular, in the case of the organic light-emittingdevice 104 both electrodes 2, 3 are formed in a transparent manner, sothat the organic light-emitting device 104 is translucent and radiatesin both directions, i.e., through the substrate 1 and through the coverlayer 9.

FIG. 3A shows an exemplified embodiment of an organic light-emittingdevice in a plan view of the active surface 11 which appears luminescentduring operation of the device. In the case of the previously shownlight-emitting devices 100 and 102 in accordance with FIGS. 1A and 1C,the active surface 11 is formed by the side of the scattering layer 7facing away from the organic functional layer stack 4, and in the caseof the light-emitting devices 101 and 103 the active surface is formedby the side of the substrate 1 (FIG. 1B) or cover layer 9 (FIG. 1D)facing away from the organic functional layer stack 4.

In order to contact at least one of the electrodes, a contact region 10is provided next to the active surface 11. Since by reason of such aone-sided electrical contact the luminous density decreases withdistance to the contact element 10 by reason of the transverseconduction resistance of the electrode materials, the scattering layerrequired for homogenization of the luminous density has a lateralvariation of the scattering effect by virtue of a varying concentrationof the scatter particles in the matrix material, which is indicated bythe differently shaded region of the active surface 11. This kind ofincrease in the scattering effect ensures that in the regions which arefurther away from the contact region 10 more light can be coupled outwhich would otherwise be guided by wave guide effects in the layers ofthe device. In particular, the concentration of the scatter particlesincreases as the distance to the contact element 10 increases.Alternatively, the thickness of the scattering layer can also increasewhen the scatter particle concentration is constant or even when thescatter particle concentration varies.

FIG. 3B shows a further exemplified embodiment for a circular organiclight-emitting device, in which the contact region 10 laterallysurrounds the active surface 11. The luminous density of the lightradiated by the active surface 11 without an optical scattering layerthus decreases from the edge towards the center. The luminous densitycan be homogenized by means of a scattering layer having a radialconcentration gradient of the scatter particles towards the center.

In order to produce scattering effect gradients, as shown in FIG. 4A ina plan view and in FIG. 4B in a sectional view, a varying density ofindividual points of the material 70 of the scattering layer can beapplied on the corresponding element 12 of the organic light-emittingdevice, e.g., on the substrate or the cover layer. By means of atempering step causing spreading of the individual regions of thematerial 70 of the scattering layer, it is possible to produce thevarying scattering film thickness of the scattering layer 7 as shown inFIG. 4B.

A further method for producing a scattering effect gradient is shown inFIGS. 5A to 5C. For this purpose, a matrix material 75 is uniformlyapplied, as shown in FIG. 5A, on an element 12 of the organiclight-emitting device, e.g., on the substrate or the cover film. Scatterparticles 76 are arranged on the matrix material 75, e.g., byspray-coating or printing, as shown in FIG. 5B, wherein the scatterparticles 76 are arranged in a desired density and varying distributionon the matrix material 75. By sinking the scattering 76 into the matrixmaterial 75, as shown in FIG. 5C, a laterally varying scatteringeffect—as described above—of the thus produced scattering layer 7 isachieved.

The invention is not limited by the description using the exemplifiedembodiments. Rather, the invention includes any new feature and anycombination of features included in particular in any combination offeatures in the claims, even if this feature or this combination itselfis not explicitly stated in the claims or exemplified embodiments.

The invention claimed is:
 1. An organic light-emitting devicecomprising: a substrate; a transparent electrode overlying thesubstrate; a further electrode overlying the substrate; an organiclight-emitting layer between the transparent electrode and the furtherelectrode; an optical scattering layer arranged on a side of thetransparent electrode facing away from the organic light-emitting layer;and a contact element, wherein at least one of the transparent electrodeand the further electrode is electrically contacted by the contactelement, wherein the optical scattering layer comprises a matrixmaterial and scatter particles having a refractive index different fromthe matrix material, wherein the scatter particles have a concentrationthat increases as a distance from the contact element increases, andwherein the optical scattering layer has a varying thickness.
 2. Thedevice according to claim 1, wherein the substrate is transparent,wherein the transparent electrode is arranged between the substrate andthe light-emitting organic layer, and wherein the optical scatteringlayer is arranged between the transparent electrode and the substrateand/or on a side of the substrate facing away from the transparentelectrode.
 3. The device according to claim 1, further comprising acover layer, wherein the transparent electrode, the further electrodeand the organic light-emitting layer are arranged between the substrateand the cover layer.
 4. The device according to claim 3, wherein thecover layer is transparent, the transparent electrode is arrangedbetween the cover layer and the light-emitting organic layer and theoptical scattering layer is arranged between the transparent electrodeand the cover layer and/or on a side of the cover layer facing away fromthe transparent electrode.
 5. The device according to claim 1, whereinthe further electrode is transparent and further scattering layers arearranged on different sides of the organic light-emitting layer.
 6. Thedevice according to claim 1, wherein the matrix material comprises oneor more of the following materials: polycarbonate, polyethylenenaphthalate, polyethylene terephthalate, polyurethane, acrylate,polymethyl methacrylate and epoxide.
 7. The device according to claim 1,wherein the matrix material comprises a sol-gel and/or an inorganicmaterial having a refractive index of greater than 1.8.
 8. The deviceaccording to claim 1, wherein the scatter particles have a size ofgreater than or equal to 200 nm and less than or equal to 5000 nm, andwherein the scatter particles are formed by pores.
 9. The deviceaccording to claim 1, wherein the scatter particles have a size ofgreater than or equal to 200 nm and less than or equal to 5000 nm, andwherein the scatter particles comprise at least one of the followingmaterials: aluminum oxide, titanium dioxide, zirconium dioxide, silicondioxide.
 10. The device according to claim 1, wherein the scatteringlayer comprises at least one additive that adapts the refractive index,is UV-absorbent and/or has a thermal conductivity that is greater thanthe thermal conductivity of the matrix material.
 11. The deviceaccording to claim 10, wherein the additive is present in form ofnanoparticles, which have a size of less than 50 nm.
 12. The deviceaccording to claim 10, wherein the additive comprises one or more of thefollowing materials: titanium dioxide, 2-hydroxybenzophenone,2-hydroxyphenyl benzotriazole, salicylic acid ester, cinnamic acid esterderivative, resorcinol monobenzoate, oxalic acid anilide,p-hydroxybenzoic acid ester.
 13. The device according to claim 10,wherein the additive comprises one or more of the following materials:aluminum nitride, silicon carbide and magnesium oxide.